The NIA supports several colonies of aged rats and mice for use in research on aging. The purpose ofthis contract is to provide independent surveillance of the health status ofNIAsupported, contractor-maintained colonies ofaged rats and mice. This contract will provide monitoring which is independent ofand in addition to the health monitoring that the colony contractor provides. The aim is to provide confirmation of results reported by the colony contractor, to serve as a research resource for resolution of questions on animal health, and to provide advice on animal health management practices. The number of animals to be tested each year is dependent on the number of contract colonies in operation each year. There are five colonies to be covered by this contract: the Fisher 344 rat colony;the multi-genotypic mouse colony;the caloric-restricted colony (rat and mouse);the hybrid rat colony;and the new mutant mouse aging colony when it is established.